Online Etymology Dictionary

ratio (n.): 1630s, "reason, rationale," from Latin ratio "reckoning, calculation, business affair, procedure," also "reason," from rat-, past participle stem of reri "to reckon, calculate," also "think" (see reason (n.)). Mathematical sense is attested from 1660.
ratiocinate (v.): 1640s, from Latin ratiocinatus, past participle of ratiocinare (see ratiocination).
ratiocination (n.): "process of reasoning," 1520s, from Latin ratiocinationem (nominative ratiocinatio) "a reasoning," from ratiocinatus, past participle of ratiocinare "to calculate, deliberate," from ratio (see ratio) + -cinari, which probably is related to conari "to try" (see conation).
ration (n.): 1550, "reasoning," later, "relation of one number to another" (1660s), then "fixed allowance of food" (1702, often rations, from French ration in this sense), from Latin rationem (nominative ratio) "reckoning, calculation, proportion" (see ratio). The military pronunciation (rhymes with fashion) took over from the preferred civilian pronunciation (rhymes with nation) during World War I.
ration (v.): "put (someone) on a fixed allowance," 1859, from ration (n.); sense of "apportion in fixed amounts" is from 1870. Related: Rationed; rationing.
rational (adj.): late 14c., "pertaining to reason;" mid-15c., "endowed with reason," from Latin rationalis "of or belonging to reason, reasonable," from ratio (genitive rationis) "reckoning, calculation, reason" (see ratio).
rationale (n.): 1650s, from Late Latin rationale, noun use of neuter of Latin rationalis "of reason" (see rational).
rationalise (v.): chiefly British English spelling of rationalize. For suffix, see -ize. Related: Rationalised; rationalising; rationalisation.
rationalist (n.): "physician whose treatment is based on reason," 1620s, from rational + -ist. Applied to a philosophical doctrine 1640s. Related: Rationalism.
rationality (n.): 1620s; see rational + -ity.
rationalization (n.): 1825, "a rendering rational," from rationalize + -ation. Psychological use is from 1908.
Of the three works now on our table, the two which we have placed first have these laudable objects in view; an improvement on the former versions of the Psalms as compositions, and the rationalization, if we may so speak, of our Church psalmody. ["The British Critic," London, Jan.-June 1825]
rationalize (v.): 1767, "to explain, to make reasonable," from rational + -ize. In the psychological sense of "to give an explanation that conceals true motives" it dates from 1922. Related: Rationalized; rationalizing.
rationing (n.): "restriction to limited allotments, as during wartime," 1918, from conditions in England during World War I, from present participle of ration (v.).
ratsbane (n.): "rat poison, arsenic," 1520s; see rat (n.) + bane.
rattan: 1650s, from Malay rotan, from raut "to trim, strip."
rattle (v.): early 14c., perhaps in Old English, but not recorded; if not, from Middle Dutch ratelen, probably of imitative origin (cf. German rasseln "to rattle," Greek kradao "I rattle"). Sense of "fluster" is first recorded 1869. Related: Rattled; rattling.
rattle (n.): c.1500, in reference to the sound, from rattle (v.). As a child's toy, recorded from 1510s.
rattlesnake (n.): 1620s, from rattle + snake (n.). Shortened form rattler is from 1827.
rattletrap: 1766, originally a noun, "nicknacks, trifles, odds and ends," from rattle (adj.) + trap, perhaps in the sense in traps (n.2). The adjectival sense of "rickety" is recorded from 1834.
ratty (adj.): 1856, "resembling a rat;" 1865, "full of rats;" 1867, "wretched, miserable, shabby," from rat (n.) + -y (2).
raucous (adj.): 1769, from Latin raucus "hoarse," related to ravus "hoarse," from PIE echoic base *reu- "make hoarse cries" (cf. Sanskrit rayati "barks," ravati "roars;" Greek oryesthai "to howl, roar;" Latin racco "a roar;" Old Church Slavonic rjevo "I roar;" Lithuanian rekti "roar;" Old English rarian "to wail, bellow"). Middle English had rauc in the same sense, from the same source.
raunch (n.): 1964, back-formation from raunchy.
raunchy (adj.): 1939, "clumsy, careless, sloppy," U.S. Army Air Corps slang, of unknown origin. Origins among cadets in Texas suggest possible connection to Mexican Spanish rancho (see ranch), which had connotations of animal filth by 1864. Sense of "coarse, vulgar, smutty" is from 1967. Related: Raunchiness.
ravage (v.): 1610s, from French ravager "lay waste, devastate," from Old French ravage "destruction," especially by flood, 14c., from ravir "to take away hastily" (see ravish). Related: Ravaged; ravaging.
rave (v.): late 14c., "to show signs of madness or delirium," from Old French raver, variant of resver "to dream, wander, rave," of unknown origin (see reverie). The identical (in form) verb meaning "to wander, stray, rove" first appeared c.1300 in Scottish and northern dialect, and is probably from an unrelated Scandinavian word (cf. Icelandic rafa). Sense of "talk enthusiastically about" first recorded 1704. Noun meaning "rowdy party" is from 1960, though rave-up was British slang for "wild party" from 1940; specific modern sense of "mass party with loud, fast electronic music and often psychedelic drugs" is from 1989. Raver, from this sense, is first recorded 1991.
ravel (v.): 1580s, "to untangle, unwind," also "to become tangled or confused," from Dutch ravelen "to tangle, fray, unweave," from rafel "frayed thread." The seemingly contradictory senses of this word (ravel and unravel are both synonyms and antonyms) are reconciled by its roots in weaving and sewing: as threads become unwoven, they get tangled.
raven (n.): Old English hræfn (Mercian), hrefn; hræfn (Northumbrian, West Saxon), from Proto-Germanic *khrabanas (cf. Old Norse hrafn, Danish ravn, Dutch raaf, Old High German hraban, German Rabe "raven," Old English hroc "rook"), from PIE root *qer-, *qor-, imitative of harsh sounds (cf. Latin crepare "to creak, clatter," cornix "crow," corvus "raven;" Greek korax "raven," korone "crow;" Old Church Slavonic kruku "raven;" Lithuanian krauklys "crow").
The common raven is easily tamed, but is mischievous and thievish, and has been popularly regarded as a bird of evil omen and mysterious character. [OED]
Old English also used hræmn, hremm. The raven standard was the flag of the Danish Vikings.
ravening: 1520s, the surviving present participle of an extinct verb raven "to prey, to plunder" (late 14c., implied in ravener), from Old French raviner (see ravenous), and is not etymologically related to raven (n.).
ravenous (adj.): early 15c., "obsessed with plundering, extremely greedy," from Old French ravinos "rapacious, violent," from raviner "to seize," from ravine "violent rush, robbery" (see ravine). Meaning "voracious, very hungry" is from early 15c. Related: Ravenously.
ravine (n.): 1760, "deep gorge," from French ravin "a gully" (1680s, from Old French raviner "to hollow out"), and from French ravine "violent rush of water, gully," from Old French ravine "violent rush, robbery, rapine," both ultimately from Latin rapina (see rapine); sense influenced by Latin rapidus "rapid." Middle English ravine meant "booty, plunder, robbery" from c.1350-1500. Cf. ravening.
raving: late 15c.; see rave; sense of "remarkable" is from 1841.
ravioli: Middle English raffyolys (mid-15c.), also rafyols. The word probably was re-borrowed several times, most recently in 1841, from Italian ravioli, a dialectal plural of raviolo, a diminutive, perhaps of rava "turnip."
ravish (v.): c.1300, "to seize (someone) by violence, carry (a person, especially a woman) away," from Old French raviss-, present participle stem of ravir "to seize, take away hastily," from Vulgar Latin *rapire, from Latin rapere "to seize, hurry away" (see rapid). Meaning "to commit rape upon" is recorded from mid-15c. Related: Ravished; ravishing.
ravishing (n.): "act of plundering," c.1300, verbal noun from ravish (v.).
ravishing (adj.): "enchanting," early 15c., from present participle of ravish (v.). The notion is of "carrying off from earth to heaven."
raw (adj.): Old English hreaw "uncooked, raw," from Proto-Germanic *khrawaz (cf. Old Norse hrar, Middle Dutch rau, Old High German hrawer, German roh), from PIE root *kreue- (1) "raw flesh" (cf. Sanskrit kravih "raw flesh," krura- "bloody, raw, hard;" Greek kreas "flesh;" Latin crudus "not cooked," cruor "thick blood;" Old Irish cru, Lithuanian kraujas, Old Church Slavonic kruvi "blood;" Old English hrot "thick fluid, serum").

Meaning "tender, sore" is from late 14c.; of persons, "inexperienced" from 1560s; "damp and chilly" first recorded 1540s. Raw material is from 1796. Phrase in the raw "naked" (1921) is from the raw "exposed flesh," attested from 1823. Raw deal "harsh treatment" attested by 1893.
ray (n.1): "beam of light," c.1300, from Old French rai (nominative rais) "ray, spoke," from Latin radius "ray, spoke, staff, rod" (see radius). Not common before 17c.; of the sun, usually in reference to heat (beam being preferred for light). Science fiction ray-gun is first recorded 1931 (but cf. Martian Heat ray weapon in H.G. Wells' "War of the Worlds," 1898).
ray (n.2): "type of fish related to sharks," early 14c., from French raie (13c.), from Latin raia, of unknown origin.
Raymond: masc. proper name, from Old French Raimund, from Frankish *Raginmund "counsel-protection" or "might-protection," from ragin "counsel, might" + mund "hand, protection" (cf. Old High German munt, Old English mund, second element in Edmund, Sigismund, etc.).
rayon (n.): 1924, chosen by National Retail Dry Goods Association of America, probably from French rayon "beam of light, ray," from rai (see ray (n.1)), which was also used in Middle English as a name for a type of cloth. So called because it is shiny. A more marketable alternative than the original patented name, artificial silk (1884), or the intervening attempt, Glos, which was "killed by ridicule" ["Draper's Record," June 14, 1924].
raze (v.): 1540s, alteration of racen "pull or knock down" (a building or town), from earlier rasen (14c.) "to scratch, slash, scrape, erase," from Old French raser "to scrape, shave," from Medieval Latin rasare, frequentative of Latin radere (past participle rasus) "to scrape, shave," perhaps from PIE *razd- (cf. Latin rastrum "rake"), possible extended form of root *red- "to scrape, scratch, gnaw" (see rodent). Related: Razed; razing.
razor (n.): late 13c., from Old French rasour "a razor" (12c.), from raser "to scrape, shave" (see raze). The use of razorback for a type of pig with a sharp ridge-like back dates from 1849.
razz (v.): "to hiss or deride," 1920, shortened and altered variant of raspberry (q.v.) in its rhyming slang sense. Related: Razzed; razzing.
razzle-dazzle (n.): 1886, American English slang, varied reduplication of dazzle (q.v.).
My confrère, The Chevalier, last month gave a new name to the scarfs of disjointed pattern when he called them the razzle-dazzle. The name was evidently a hit of the most patent character, for in several avenue and Broadway stores the clerks have thrown out a display of broken figures before me and explained that the ruling style at present was the razzle-dazzle, and the word seems to have been equally effective with the public, for when it is quoted by the live salesman, the customer, I am told is at once interested and caught by it. ["Clothier and Furnisher" magazine, Jan. 1889]
razzmatazz: 1894, perhaps a varied reduplication of jazz (n.). The word had early associations with that kind of music (later especially in contrast to swing).
re: "with reference to," 1707, from Latin in re "in the matter of," ablative case of res "matter, thing." Its use in English is execrated by Fowler in three different sections of "Modern English Usage."
re-: word-forming elementx meaning "back to the original place, again," also with a sense of "undoing," c.1200, from Old French and directly from Latin re- "again, back, against." Often merely intensive.
re-elect (v.): also reelect, c.1600, from re- "back, again" + elect (v.). Related: Re-elected; re-electing.
re-enact (v.): also reenact, 1670s, from re- "back, again" + enact. Originally of laws, etc.; meaning "to perform again, reproduce" is recorded from 1854. Related: Re-enacted; re-enacting.
re-enactment (n.): also reenactment, 1803; see re-enact + -ment.